Solution to 1996 Problem 5

The only horizontal forces on the car are the force of air resistance and the force of the road. Because the car travels at a constant velocity, the sum of these two forces must have a magnitude of mv^2/r and it must point towards the center of the circle. If you add the forces \mathbf{F}_A, \mathbf{F}_B, \mathbf{F}_C, \mathbf{F}_D, \mathbf{F}_E to the force \mathbf{F}_{air} one at a time, it is clear that the only \mathbf{F}_{air} + \mathbf{F}_C could possibly point toward the center of the circle. Therefore, answer (C) is correct.

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